Impacts of the Variations of Aerosols Components and Relative Humidity on the Visibility and Particles Size Distribution of the Desert Atmosphere

Abstract

This paper investigates the Impact of relative humidity, varying the concentrations of water-soluble aerosol particle concentrations (WASO), Mineral Nuclei Mode Aerosols Particle Concentration (MINN), mineral accumulation mode, nonspherical (MIAN) aerosol particles concentrations and Mineral Coarse Mode Aerosols Particle Concentration (MICN) on the visibility and particles size distribution of desert aerosols based on microphysical properties of desert aerosols. The microphysical properties (the extinction coefficients, volume mix ratios, dry mode radii and wet mode radii) were extracted from Optical Properties of Aerosols and Clouds (OPAC 4.0) at eight relative humidities, RHs (00 to 99%) and at the spectral visible range of 0.4-0.8mm, the concentrations were varied to obtain five different models for each above-mentioned component. Regression analysis of some standard equations were used to determine the Angstrom exponent (α), the turbidity coefficient (β), the curvature (α2), humidification factor (), the mean exponent of aerosol growth curve (µ) and the mean exponent of aerosol size distributions (n). The values of angstrom exponent (α) were observed to be less than 1 throughout the five models at all RHs for the four studied components, and this signifies the dominance of coarse mode particles over fine mode particles. But the magnitude of the angstrom exponent (α) fluctuates all through the studied components except for WASO which increased with the increase in RH across the models and this also signifies the dominance of coarse mode particles with some traces of fine mode particles. The investigation also revealed that the curvature (α2) has both monomodal (negative signs) and bimodal (positive signs) types of distributions all through the five models and this also signifies the dominance of coarse mode particles with some traces of fine mode particles across the individual models for all the studied components. it was also found that the visibility decreased with the increase in RH and increased with the increase in wavelength. The investigation further revealed that the turbidity coefficient (β) fluctuates with the increase in RH and the particles concentrations, and this might be due to major coagulation and sedimentation. The analysis further found that there is a direct inverse power relation between the humidification factor and the mean exponent of aerosols size distribution with the mean exponent of aerosols growth curve. It was also found that as the magnitude of µ increased for MIAN, MINN and MICN, the effective hygroscopic growth decreased. For WASO, it was found that as the magnitude of µ decreased, the effective hygroscopic growth increased with the increase in particles concentrations and RH. The decreased in the magnitude of µ for WASO might be due to the fact that as we increase the non-hygroscopic particles, we decrease the deliquescence. The mean exponent of aerosol size distribution (n) being less than 3 shows foggy condition of the desert atmosphere the four investigated components and five studied models.

Impacts of the Variations of Aerosols Components and Relative Humidity on the Visibility and Particles Size Distribution of the Desert Atmosphere: Validating Results Obtained from OPAC 4.0 using MERRA-2 Model (Angstrom Exponent and Extinction Coefficient) Data

“…The OPAC programming software comprises of two sections, the initial segment is a dataset of microphysical properties and the subsequent optical properties of cloud and aerosols components at various wavelengths and for different relative humidity conditions [4], [9][10][11], [23], [28]. The other part is a FORTRAN program that permits the user to separate information from this dataset, to compute extra optical properties, and to ascertain optical properties of the mixtures of the stored cloud and aerosols components.…”

“…It is well know that particulate matter is also generated from mineral dust [8]. Residue from the Sahara is the biggest source of mineral dust in the atmosphere [8][9][10]. It is a wonder of interest for meteorological material science as well as for general wellbeing too, because of the potential health effect of its air dispersal and flow in the atmosphere [11], [12].…”

“…In the natural environments the changes in the microphysical and optical properties observed at a given wavelength with respect to the corresponding change in relative humidity is a signs that measuring condition have changed [4], [9][10][11]. These changes can cause unbalance in the atmosphere by causing decrease in visibility or other harmful effects to man and his environment [10].…”

“…In the natural environments the changes in the microphysical and optical properties observed at a given wavelength with respect to the corresponding change in relative humidity is a signs that measuring condition have changed [4], [9][10][11]. These changes can cause unbalance in the atmosphere by causing decrease in visibility or other harmful effects to man and his environment [10]. Many of the papers published to date that provide information on health/environmental related mineral and Saharan dust research have focused on the impact of anthropogenically generated mineral or airborne dust related (such as PM generated by combustion engines) [13], while relatively little work has looked at the impact of variations of the meteorological parameters and micro physical properties of the naturally generated dust (such as all forms of dust emanating from dust storms).…”

“…In this work, average aerosol extinction coefficient and average Angstrom Exponents (α) extracted from MERRA-2 Model data (for 10 selected deserts across the world) at 550nm and an average RH of 78% from 2010 to July 2021 was used to validate results obtained from simulations carried out using OPAC 4.0 in our previous work [10] using time series analysis.…”